A vehicle power transmitting apparatus is required not only to transmit power from an engine to a wheel but to enable radial and axial displacements or moment displacement of the wheel caused by bounce of the vehicle during rolling on a rough road or during turning of the vehicle. Accordingly, one end of a driving shaft, arranged between the engine and the driving wheel, is connected to a differential gear unit, via a sliding type constant velocity universal joint. The other end is connected to the driving wheel, via a bearing apparatus. The driving wheel includes a non-sliding type constant velocity universal joint.
Several types of structures of the wheel bearing apparatus have been proposed. One type is shown in FIG. 4. Here, the driving wheel bearing apparatus 50 has a wheel hub 51 adapted to mount a wheel (not shown) at one end. A double row rolling bearing 52 rotatably supports the wheel hub 51. A secured type constant velocity universal joint 53 transmits the power of the driving shaft (not shown) to the wheel hub 51.
The wheel hub 51 has an integrally formed wheel mounting flange 54. Its outer circumferential surface is formed with an inner raceway surface 51a. A cylindrical portion 51b axially extends from the inner raceway surface 51a. The double row rolling bearing 52 has an outer member 55 integrally formed with a body mounting flange 55b on its outer circumferential surface. A double row outer raceway surfaces 55a, 55a is formed on its inner circumferential surface. An inner member 57 is inserted into the outer member 55 via double row rolling elements (balls) 56, 56, contained within the outer member 55.
The inner member 57 include the wheel hub 51. An inner ring 58 is press-fit onto the axially extending portion 51b of the wheel hub 51. The inner ring 58 is formed with an inner raceway surface 58a on its outer circumferential surface. The inner ring 58 is axially immovable secured relative to the wheel hub 51 by a caulked portion 51c. The caulked portion 51c is formed by plastically deforming, radially outwardly, the end portion of the axially extending portion 51b of the wheel hub 51.
The constant velocity universal joint 53 includes a mouth portion 59. An outer joint member 62 is integrally formed with a shoulder 60 that forms the bottom of the mouth portion 59. A shaft portion 61 extends from the shoulder 60. The outer joint member 62 is inserted into the inner member 57 (wheel hub 51) in a manner to enable torque transmission between the two. That is, serrations 63 formed on the inner circumferential surface of the wheel hub 51 mate with serrations 64 formed on the outer circumferential surface of the shaft portion 61 of the outer joint member 62. The shaft portion 61 of the outer joint member 62 is inserted into the wheel hub 51 until the shoulder 60 of the outer joint member 62 abuts against the caulked portion 51c. The wheel hub 51 and the outer joint member 62 are joined together so as not to be axially separated by fastening a securing nut 66, at a predetermined fastening torque, on an external thread 65 formed on the end of the shaft portion 61.
It is known that a large torque is applied from the engine to the driving wheel via a sliding type constant velocity universal joint (not shown) at a time of increasing engine speed (at the time of starting the vehicle and thus torsion is caused on the drive shaft). Accordingly, torsion is also caused on the inner member 57 of the double row rolling bearing 52 that supports the driving shaft. When the large torque is caused on the drive shaft, stick-slip noise is caused by sudden slip between the mutually abutting surfaces of the outer joint member 62 and the inner member 57. The slips are caused by a circumferential gap between the serrations 63 of the wheel hub 51 and the serrations 64 of the shaft portion 61 of the outer joint member 62.
In order to deal with this problem, the prior art vehicle wheel bearing apparatus 50 has the end surface of the caulked portion 51c of the wheel hub 51, against which the shoulder 60 of the outer joint member 62 abuts, finished as a flat surface 67. This makes it possible to bring surface contact between the caulked portion 51c and the shoulder 60. Thus, this reduces the surface stress applied to the caulked portion 51c by the fastening force of the nut 66. Accordingly, it is possible to prevent plastic deformation of the caulked portion 51c as well as loosening of the nut 66. Thus, this prevents the generation of the stick-slip noise due to sudden slip between the abutting surfaces of the shoulder 60 and the caulked portion 51c (see Japanese Patent No. 3533883).